In
the article Field
Growing it was established that for a thick trunked bonsai,
the tree must first be allowed to grow freely in the ground or
a pot to help thicken the trunk.

Having
thickened the trunk by allowing free growth for a number of years,
it is unlikely that the trunk have much taper and will often lack
any movement.

There
are a number of ways of introducing taper and movement to a field
grown trunk; this article describes one method that is known to
be widely used in Japanese growing fields to 'build' myogi or informal upright trunks for bonsai. This process can equally
be applied to a collected or nursery tree that is currently too
tall for use as a bonsai and needs to be reduced in height.

By
studying the following images, it is hoped that the reader will
understand and use some of the techniques described to introduce
taper and movement in the trunks and new branches for their trees.

This
method is intended for deciduous trees only but some of its principles
can be applied to coniferous species.

Image
1 shows the lower portion of the trunk of a tree growing in
the ground. its girth is adequate for use as a bonsai but there
is little movement or taper.

Ideally,
the finished bonsai will be approximately 6 times
the height of the trunk diameter. The diameter of this trunk is
3" so the ideal height of the tree when it is finished will
be 18". If a taller bonsai is required, this tree will need
growing on for further years before this process begins. Once the trunk has been chopped, it will barely thicken
until the new section above it has all but reached the same girth
and at which point, taper is all but lost. Refer
to this article for an example

So
the projected final height of this tree will be 18". The
first branch should be at approximately a 1/3 of the overall
height. This means that the first branch should be 6" from
the base of the tree.

Image
2. Late Winter/early Spring. The trunk is chopped with
a straight cut at a height of around 12", approximately
2/3 the height of the finished tree. If additional movement is
required on a very straight lower trunk, the chop can be made
at 6" or 1/3 of the height of the tree.

A straight cut reduces moisture loss and potential dieback; until
a new shoot has appeared and been chosen as the new leader, there
is no point in making a diagonal cut as is sometimes advised.
As with all cuts, the chop should be sealed with cut paste.

Image
3. Autumn. The tree drops its leaves and reveals the effects
of a growing season left to grow freely. The
heavy chopping has resulted in strong budding from all over the
trunk.